The present invention relates to a safety system for detecting abnormality in a control system of an automotive engine and for stopping the engine.
Japanese Patent Application No. Laid-Open 61-8435 discloses an abnormality detecting system where a throttle position detecting means is provided for detecting the degree of of a throttle valve and an accelerator pedal position sensor is provided for producing an accelerator pedal depression signal dependent on the degree of depression of the accelerator pedal. When the throttle position detecting means produces an output signal representing an opening of the throttle valve while the accelerator pedal depression signal is zero, the system determines that the throttle position detecting means broke down.
However, in an engine control system where a throttle valve is driven by a stepper motor in accordance with the depression degree of the accelerator pedal, such an abnormality detecting system is improper. If an operating system for the stepper motor breaks down, the throttle valve can not be controlled. It causes a dangerous situation such that engine speed extremely increases.